Record-High Organic Device Performance enabled by Polymorphism in Organic Semiconductors

有机半导体薄膜加工方法的最新发展使得非平衡态多晶的稳定性大大提高了电气器件的性能。这些进展突出了控制多态性的重要性，以最大限度地提高给定材料的性能。然而，到目前为止，还没有办法预测哪种材料的多态性是可以预期的，以及不同的多态性可以提供什么样的电气性能。作为可能的结果，许多材料，无论是现有的还是尚未合成的，已经或将被宣布在设备中表现不佳，仅仅是因为它们没有以产生（未知的）高性能多晶片的方式加工。为了纠正这种情况，我们建议建立一个理论框架来预测小分子有机半导体的多态性，并根据其预测的电学性质对潜在的多态性进行排序。作为补充，我们将采用一种特殊的印刷方法来检测和稳定印刷薄膜中可溶性有机材料的多晶形式，这将为待开发的理论提供非常必要的实验基准和校准参考。将使用各种实验工具来精确确定印刷薄膜中的分子包装，从而为理论提供有价值的反馈。理论方法将建立分子结构和电性能之间的直接联系，通过考虑许多不同的多晶，而不是采用传统沉积技术时通常遇到的热力学平衡中的多晶。该方法创造了一整套可能的结构实现，具有预期的更高的载流子迁移率，对某些分子来说可能是数量级的。在实验部分，我们将测试这个新理论所做的预测，特别是那些它表明具有高技术相关性（高载流子迁移率）的预测。我们将使用现代沉积技术来介绍沉积条件的可变性，这是实现这种多晶型所必需的。材料将被表征，电子设备将被分析并与理论进行比较。拟议的面向设备的模拟框架将基于一组有限的结构开发，但通常适用，并且是一种战略工具，可以激发大量新的高迁移率材料，否则这些材料将仍然未被发现。这将极大地改变材料分析和设计的方式，并将催化从合成到设备测量的整个链条的研究。

Recent developments in thin film processing methods for organic semiconductors have allowed the stabilization of non-equilibrium polymorphs with drastically better electrical device performance. These advances highlight the importance of controlling polymorphism to maximize the performance of a given material. However, so far there is no way to predict for which materials polymorphism can be expected and what electrical performance the different polymorphs can deliver. As a likely result, many materials, both existing and yet to be synthesized, have been or will be declared poorly performing in devices simply because they are not processed in a way that produces films of the (unknown) high-performance polymorph(s). In order to remedy this situation, we propose to develop a theoretical framework to predict polymorphism in small molecule organic semiconductors and to rank potential polymorphs based on their predicted electrical properties. In a complementary effort, we will employ a special printing method to detect and stabilize polymorphic forms of soluble organic materials in printed thin films, which will provide the very necessary experimental benchmarks and calibration references to the to-be-developed theory. Various experimental tools will be used to precisely determine the molecular packing in the printed films thus providing valuable feedback to theory.The theoretical approach will establish a direct link between molecular structure and electrical performance by considering many different polymorphs beyond the one in thermodynamic equilibrium that is usually encountered when employing conventional deposition techniques. The approach creates a whole set of possible structural realizations with expectedly higher carrier mobilities, possibly by orders of magnitude for some of the molecules. In the experimental part, we will test the predictions made by this new theory, especially those that it suggests to be of high technological relevance (high charge carrier mobility). We will use modern deposition techniques to introduce the variability in deposition conditions which is necessary to realize such polymorphs. Materials will be characterized and electronic devices will be analyzed and compared to theory.The proposed device-oriented simulation framework will be developed based on a restricted set of structures but is generally applicable and is a strategic tool that could spark a vast amount of novel high-mobility materials that would otherwise remain undiscovered. This could significantly transform the way of performing material analysis and design and should catalyze the research along the whole chain from synthesis to device measurements.